Internal combustion engines generally have an engine block with multiple engine cylinders arranged in series. The cylinders are cooled by coolant flowing through an adjacent coolant jacket. The coolant jacket includes a coolant jacket wall approximately parallel to the cylinder wall, defining a coolant passage therebetween.
Coolant enters the engine block at one end, flows through the coolant passage along both sides of the cylinders, exits the block at the opposing end, and transfers up into the cylinder head to flow through the head. This is referred to as a "U-flow" pattern. Alternatively, the coolant may flow through the head first before transferring to the block. While U-flow provides balanced heat transfer cylinder-to-cylinder because it provides a consistent coolant mass flow rate past each cylinder, it may not provide uniform heat transfer around each individual cylinder.
Some engine blocks include cooling slots between adjacent cylinders, allowing coolant to flow around the whole outer circumference of the cylinders to provide more consistent heat transfer from the cylinder wall. In siamese engine blocks where adjoining cylinders share a common cylinder wall therebetween to conserve lengthwise packaging space required for the engine block, a cooling slot is not included and coolant cannot flow between the cylinders. Therefore, heat transfer out of the cylinder is not as efficient in the circumferential area of the common cylinder wall.
Since the cylinder wall and coolant jacket wall determine the coolant passage shape, a horizontal section therethrough translates into repeated arcs in a Siamese engine block. Where adjacent cylinders meet at their shared cylinder wall, a vertical V-shaped groove is defined which creates a V-bend in the coolant passage. The liquid flow through the V-bend area is reduced due to the bend in the flow path. This stagnant flow translates into a reduced rate of heat dissipation in the common wall between the adjoining cylinders. A minimum coolant flow rate of approximately 1.5 meters/second is needed to provide the desired convective heat transfer from the cylinder walls when the engine is operating at peak torque.
A constant rate of cooling throughout the block is desired to reduce the effects of local thermal expansion such as distortion between a cylinder bore and its piston which may cause increases in oil consumption. Further, overall heat transfer from the piston improves piston ring durability and reduces spark knock tendencies.
A further consideration for the cooling system is the volume of coolant pumped throughout the engine. The more coolant a system demands for adequate cooling, the greater capacity coolant pump is needed. In addition, during engine cold starts, the more coolant there is, the longer it takes for the engine to warm to the optimum operating temperature.
Therefore it is desirable to optimize an engine block to promote adequate coolant flow therethrough and in particular in the V-bend area of the coolant passage where adjoining cylinders meet for uniform heat transfer about an individual cylinder, while minimizing the system volume of coolant required.